JPH04130195A - Lubricant for hot rolling of common steel or special steel - Google Patents

Abstract

PURPOSE:To obtain the title lubricant which can prevent the seizure to rolling rolls when common steel, special steel, etc., are hot-rolled under a high load by dispersing specified fine inorganic particles in a viscous aqueous solution. CONSTITUTION:1-30wt.% fine inorganic particles of which particles having a diameter of 10mum or smaller account for at least 90wt.% and which comprise a compound selected from MoS2, BN, PbO, PbS, CaF2, alumina, titania, graphite, iron oxide, nickel oxide, chromium oxide, and an inorganic silicate are dispersed in a viscous aqueous solution, if necessary, having a water-soluble high-molecular thickening agent incorporated therein, having a viscosity of 1X10<3> to 5X10<5>cP to give the title lubricant.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a lubricant for hot rolling that suppresses seizing on rolling rolls, particularly when hot rolling ordinary steel, special steel, etc. under high loads. .

[Prior Art] When hot-rolling various steel plates, if the rolled material seizes on the rolling rolls, flaws will occur on the circumferential surface of the rolling rolls, and these flaws will be transferred to the rolled material to become surface flaws. When such surface flaws occur, even if they are minor, the material becomes unsuitable for use in mirror finishing applications where surface texture is important. As a result, the uses of the obtained steel sheet are subject to restrictions.

Further, it is necessary to perform surface care of a steel plate with surface flaws in a polishing process. Furthermore, if the degree of flaw is significant,
It cannot be shipped as a product and becomes scrap.

This results in a decrease in yield and an increase in manufacturing costs.

Regarding surface flaws caused by seizure, various methods have been studied to suppress their occurrence.

[Problems to be Solved by the Invention] The occurrence of surface flaws due to roll seizure is particularly problematic in hot rolling of stainless steel sheets. For example, in stands 1 to 3 of the finish rolling mill group of a tandem mill with a large rolling load, the amount of plastic deformation is large, so the oxide film formed on the surface of the rolled material is destroyed, and the metal-to-metal gap between the rolling rolls is destroyed. Contact occurs and seizure is likely to occur.

This seizure phenomenon occurs not only in hot rolling of stainless steel sheets but also in hot rolling of ordinary steel and special steel. Particularly in recent years, there has been a tendency to increase the rolling reduction per pass in order to increase the productivity of hot rolling lines and improve material quality. As a result, the rolling load increases, making it more likely that seizure will occur. Furthermore, increases in rolling speed and decreases in idle time tend to increase the temperature of the rolling rolls and promote seizure.

Under these circumstances, schedule-free rolling and mixed rolling of different steel types are becoming more popular, and prevention of roll seizure has become an important issue. In this point,
As mentioned above, various attempts have been made to prevent surface flaws caused by seizure by improving lubricants, but at present no sufficient anti-seizure effect has been achieved. In other words, existing animal or vegetable oils, mineral or synthetic lubricants, etc. are present between the rolling roll and the rolled material and have the effect of lowering the coefficient of friction, but they are not sufficient to prevent seizure. No effect is obtained.

Therefore, the present invention uses, as an alternative to these conventional lubricants, a substance that prevents metal-to-metal contact between the material to be rolled and the roll, and also has a lubricating effect, thereby reducing the heat applied to the roll. The purpose is to produce rolled products with no sticking and excellent surface quality.

[Means for Solving the Problems] In order to achieve the object, the hot rolling lubricant of the present invention contains Mo Ss, BN, P b O, P b S,
CaFx, graphite, iron oxide, alumina,
1 to 3 inorganic fine particles of one or more selected from titania, nickel oxide, chromium oxide, and inorganic silicate.
It is characterized by being dispersed in a viscous aqueous solution at a ratio of 0% by weight.

Here, it is preferable to use inorganic fine particles in which 90% by weight or more is fine powder with a particle size of 10 LLm or less. In addition, a water-soluble polymer thickener is added to the viscous aqueous solution to increase the viscosity to I
It is preferable to adjust it to 103 to 5X10'cP.

[Function] The cause of surface flaws on steel materials during hot rolling is that the rolled material seizes on the rolling rolls and the seizure is repeatedly transferred to the rolled material. For this reason, it is not possible to freely perform rolling operations by switching steel types, which reduces production efficiency. In addition, rolling rolls with seizures are
Rolls must be replaced with rolls with better surface properties, which inevitably lowers operating efficiency due to increased roll consumption and increased rolling down time.

The present inventors have been conducting research on roll seizure during hot rolling of various steel materials including stainless steel for many years. During this time, we have experienced that roll seizure tends to occur during high-speed rolling under high pressure as slabs increase in size, and is particularly noticeable when the steel type of the rolled material is changed. This is due to the fact that when rolling under high loads, the oxide film that has formed on the surface of the rolled material is destroyed, and there is not enough time to form a scale layer that protects the newly formed surface. It turned out that it was possible.

Problems are particularly common in tandem mills with high rolling speeds, and there are fewer cases of surface defects in Stetskell mills, etc.
This shows the importance of the protective effect of scale.

Therefore, the present inventors have considered preventing seizure by replenishing the missing scale from the outside and preventing metal-to-metal contact between the material to be rolled and the rolling roll.

In this series, JP-A-64-83309 introduced the use of iron oxide powder dispersed in a viscous aqueous solution as a lubricant for hot rolling of stainless steel.
JP-A-1-167396 introduced the use of graphite powder similarly dispersed in a viscous aqueous solution as a lubricant for hot rolling of stainless steel.

When using this type of lubricant, even when using a high Cr roll as a work roll, which has good compatibility with stainless steel, which is the material to be rolled,
Roll seizing of stainless steel can be prevented even when hot rolling is performed at high temperatures of 10 to 50 kgf/mm'' while applying a high load of 10 to 50 kgf/mm''.

Subsequently, the present inventors investigated and researched substances other than iron oxide powder and graphite in order to prevent seizure by further avoiding metal-to-metal contact. The possibility of adopting this method for hot rolling was investigated. As a result, Mo Sz, B N
, P b O, P b 5CaFa, graphite,
It was discovered that iron oxide, alumina, titania, nickel oxide, chromium oxide, inorganic silicate, etc. function as similarly effective lubricant components, leading to the present invention. Note that these inorganic fine particles may be dispersed in the viscous aqueous solution alone or in combination.

The amount of inorganic fine particles dispersed in the viscous aqueous solution must be maintained at 1 to 30% by weight. This amount of dispersion is 1% by weight.
If it is less than that, the anti-seizure effect due to the addition of inorganic fine particles will be small. Conversely, in the case of a viscous aqueous solution in which fine inorganic particles are dispersed in an amount exceeding 30% by weight, it is required to significantly increase the ejection energy when spraying the aqueous solution onto a rolling roll. This not only impairs economic efficiency, but also tends to cause troubles such as clogging of conduits due to precipitation and volume of inorganic fine particles.

Further, the particle size of the inorganic fine particles is preferably such that 90% by weight or more has a particle size of 10 μm or less in order to maintain a homogeneous dispersion state in an aqueous solution. 90% by weight or more has a particle size of 10μ
m or less, a homogeneous dispersion state is maintained even after an aqueous solution in which inorganic fine particles are dispersed is left for one week. Further, by reducing the particle size, a good dispersion state can be obtained even in a relatively low viscosity water droplet liquid. Furthermore, by reducing the particle size, it is possible to suppress the adverse effects of inorganic fine particles on the surface of the steel material.

The viscosity of the aqueous solution in which the inorganic fine particles are dispersed can be adjusted to have a viscosity of 1×101 to 5×1 by adding a water-soluble polymer thickener.
It is preferable to adjust to 0' cP (centipoise). When the viscosity is maintained within this range, adhesion to the mill rolls is adequate.

Among the inorganic fine particles, molybdenum disulfide M o S 2 is known as a solid lubricant having a layered structure that is easily sheared. When this is supplied to the hot rolling rolls, metal-to-metal contact is prevented while making use of the lubricity, and an anti-seizure effect can be obtained.

Boron nitride BN has a helical layered crystal structure and is known as a substance having the same lubricating effect as molybdenum disulfide. Furthermore, it has a high melting point of 3000°C and is a substance with excellent high-temperature stability. Therefore, it exhibits a great effect of suppressing metal-to-metal contact between the rolled material and the rolling roll.

Graphite has a layered structure in which hexagonal plate-shaped crystals are connected, and its decomposition temperature is as high as 3498°C. Therefore, even at the hot rolling temperature of the steel material to be rolled, the initial state is sufficiently stably maintained, and moreover, sliding deformation occurs on the inter-fold surface to reduce the coefficient of friction. It is also used as an effective substance that prevents metal-to-metal contact between the material to be rolled and the rolling rolls and exhibits a lubricating effect.

Lead oxide PbO and lead sulfide PbS have relatively low melting points;
In the hot rolling temperature range of steel, it is in a molten or semi-molten state. By covering the surface of the rolling roll with this melt, the metal
Metal contact is avoided and seizure is prevented.

Calcium fluoride Ca F 2 has a high melting point of 1373° C., exhibits excellent lubricity at high temperatures, prevents metal-to-metal contact, and suppresses seizure on rolling rolls.

Iron oxide, alumina A 12 z Os, titania Ti0
- Nickel oxide Ni○, chromium oxide Cr20x, etc. are all hard oxides that are stable at high temperatures. Note that the iron oxide may be used in the form of one type, such as Fed, Few O, or Fei 04, or a mixture of two or more types. These oxides are effective in improving the lubrication effect of MoS2. B
Slightly more than N, Pbo, Pbs, etc. However, forming a stable oxide film between the rolled material and the rolling roll prevents metal-to-metal contact between the two, which has a large effect on seizure prevention. In addition, since the amount of lubricant supplied to the surface of the rolled material is small, even if it remains on the surface of the rolled material even though it is a hard oxide, it will not wear out the rolling rolls. There is little risk that it will be promoted. Furthermore, since it is a stable oxide, it does not penetrate into the rolled material (it is easily removed in the subsequent pickling process, and it does not adversely affect the pickling properties).

Inorganic silicates are composite oxides of silica and metal oxides, and typical examples include mica and glass. Many inorganic silicates are in a molten state in the hot rolling temperature range of steel materials, and form a film on the surface of the rolling roll as a melt, thereby avoiding direct contact with the rolled material.

Furthermore, the type of water-soluble polymer thickener added to adjust the viscosity of the viscous aqueous solution is not particularly limited. However, when considering the corrosivity of the lubricant when it scatters and adheres to surrounding rolling equipment, a neutral or weakly alkaline lubricant is preferable. Furthermore, it is preferable to use a thickener that exhibits stable viscosity even when the pH of the lubricant is adjusted. Examples of such thickeners include acrylic acid polymers and carboxyvinyl polymers.

[Examples] Hereinafter, the present invention will be specifically described by way of examples with reference to the drawings.

Ordinary steel plate with a thickness of 25 mm, width of 50 mm, and length of 250 mm (C: 0.15%, Si: 0.68%, Mn: 1.5
3%, Pro, oos%, S: 0.001%) and special steel plate (C: 0.81%, Si: 0.20%, Mn:
0.41%, P: 0.016%, Sho, 004%
, Ni: 1.77%, Cr: 0.38%) was hot rolled by one-pass rolling at a rolling temperature of 850° C. and a rolling reduction of 70%. At this time, the rolling roll is
A roll made of hot work tool steel 5KD61 was used.

Further, the material to be rolled was heated in an inert gas.

A lubricant was sprayed onto the surface of a rolling roll with a diameter of 350 mm and a barrel length of 300 mm before hot rolling. That is, as shown in FIG. 1, the lubricant contained in the lubricant container 1 is sent to the injection nozzle 3 through the supply conduit 2 using a pump with a pressure of 100 kg f / cm2, and is injected. A fine lubricant liquid 11i4 was injected from the nozzle 3 onto the circumferential surface of the rolling roll 5 rotating at 40 rpm. The spray width was set to 200 mm, and the spray time was set to 3 seconds.

As a result, a total weight of 5 g of lubricant was supplied to the circumferential surface of the rolling roll 5. This amount corresponds to forming a liquid film with a film thickness of approximately 2 OLLm.

After injecting the lubricant onto the circumferential surface of the rolling roll 5, the water contained in the high-pressure water container 6 is pumped through the nozzle 7 at a pressure of 3 kgf.
/cm” as water droplets 8. This water supply was as follows:
This corresponds to the supply of roll cooling water to the hot rolling mill. If the viscosity of the lubricant is appropriate under the conditions in which the water droplets 8 are sprayed, the rate at which the water droplets 8 will run down will be low.
Increases the adhesion rate of lubricant to

As shown in Table 1, the lubricant has an average particle size of 1.1
A viscous aqueous solution containing various inorganic fine particles having a maximum particle size of 5 μm or less and an acrylic acid polymer as a thickener was used. After rolling, the surfaces of the rolling roll 5 and the rolled material were inspected to determine whether or not seizure occurred. The results are shown in Table 1.

As is clear from Table 1, Mo5x according to the invention,
A lubricant containing BN, Pbo, PbS, CaFa, etc. exhibits a sufficient anti-seizure effect, making it possible to produce rolled steel sheets with excellent surface properties.

BN to be dispersed in a viscous aqueous solution, Aj2. The stability of fine particle dispersion was investigated in lubricants prepared by varying the amount of inorganic fine particles such as O, etc. and the viscosity of the viscous aqueous solution. The stability is
After preparing the lubricant, it was placed in a beaker and allowed to stand, and the state of dispersion of the fine particles after one week was evaluated. As an investigation method, a lubricant sample was taken from the upper part of the beaker, the content of fine particles contained in the sample liquid was measured, and the ratio to the content at the initial stage of preparation was determined.

Note that, as in Example 1, as the inorganic fine particles, those having an average particle size of 1.1 μm and a maximum particle size of 5 μm or less were used.

Furthermore, an acrylic acid polymer was used as a thickener for the viscous aqueous solution.

The results of the investigation on fine particle dispersibility are shown in Table 2.

(Hereinafter, the margin of this page) As is clear from Table 2, the amount of dispersion of inorganic fine particles is
As long as the lubricant aqueous solution in the upper layer of the beaker is maintained at ~30% by weight, and as long as the viscosity of the viscous aqueous solution is maintained at 1 x 10 s - 5 x 105 cP, the inorganic fine particles contained in the lubricant aqueous solution in the upper layer of the beaker will remain intact even after being left for one week. The content was the same as the initial one. That is, it can be seen that no precipitation of fine particles occurred and a stable dispersion state was obtained.

This shows that lubricant can be supplied to rolling rolls under stable conditions over a long period of time without clogging caused by precipitation or accumulation of inorganic particles in the lubricant supply conduit or supply nozzle. .

[Effects of the Invention] As explained above, when the lubricant of the present invention is used, a stable lubricant film is formed on the circumferential surface of the rolling roll, and the metal-metal gap between the rolling roll and the rolled material is Contact can be avoided. As a result, the rolled material is prevented from seizing on the circumferential surface of the rolling rolls, and a hot-rolled steel sheet without defects such as surface flaws is obtained.This hot-rolled steel sheet has excellent surface properties that limit its use. It can be used in a wide range of fields without any damage.Furthermore, since the work load of surface care in subsequent processes is eased, manufacturing costs can also be reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a mechanism for spraying lubricant onto rolling rolls. 1: Lubricant container 2: Supply conduit 3: Spray nozzle 4: Lubricant droplet 5: Rolling roll 6: High pressure water container 7: Cooling water nozzle 8: Water droplet

Claims (3)

[Claims] (1) MoS_2, BN, PbO, PbS, CaF_2
, alumina, titania, graphite, iron oxide, nickel oxide, chromium oxide, and inorganic silicate, one or more types of inorganic fine particles are dispersed in a viscous aqueous solution at a ratio of 1 to 30% by weight. A lubricant for hot rolling of ordinary steel or special steel, characterized by: (2) A lubricant for hot rolling of ordinary steel or special steel, wherein 90% by weight or more of the inorganic fine particles according to claim 1 are fine powders having a particle size of 10 μm or less. (3) A heat treatment for ordinary steel or special steel, characterized in that a water-soluble polymer thickener is added to the viscous aqueous solution according to claim 1, and the viscosity is adjusted to 1 x 10^2 to 5 x 10^5 cP. Lubricant for inter-rolling.